Better Understanding of "Winter Blues"

Seasonal affective disorder, or SAD, is a mood disorder characterized by depression related to a certain season of the year - especially winter. However, SAD is often not described as a separate mood disorder but as a "specifier," referring to the seasonal pattern of major depressive episodes that can occur within major depression and manic depression.

PET Scanning Used to Measure Serotonin

In the first study of its kind, the team at the Centre for Addiction and Mental Health (CAMH) in Toronto, Ontario, used positron emission tomography (PET) to determine that brain levels of serotonin transporters are significantly higher in fall/winter than in spring/summer.

PET is a type of nuclear medicine procedure. These studies evaluate the metabolism of a particular organ or tissue, so that information about the physiology (functionality) and anatomy (structure) of the organ or tissue is evaluated, as well as its biochemical properties.

Serotonin is involved in regulating emotional functions such as mood and energy levels, and physical functions such as eating and energy balance.

Serotonin transporters remove serotonin, so the findings suggest there is more serotonin removal in the fall/winter than in the spring/summer, say the researchers. They also found that higher serotonin transporter binding (the process that removes serotonin) values occur at times when there is less sunlight.

Better Understanding of Seasonal Affects

The study - the first to identify seasonal differences in brain levels of serotonin transporter levels - may help improve understanding of seasonal mood changes in healthy people, vulnerability to seasonal affective mood disorders, and the relationship of light exposure to mood.

This is "an important lead in understanding how season changes serotonin levels. This offers an explanation for why some healthy people experience low mood and energy in the winter, and why there is a regular re-occurrence of depressive episodes in fall and winter in some vulnerable individuals. The next steps will be to understand what causes this change and how to interfere with it," study author Dr. Jeffrey Meyer says.

"Over the following years, we intend to determine the specifics of the environment [such as light exposure] that influence serotonin transporter levels so as to determine what is the optimal environment to prevent illness. In the future, it may be that just like we have lifestyle recommendations to prevent heart disease, we will have lifestyle recommendations to prevent major depressive disorder," Dr. Meyer says.

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More about Seasonal Affective Disorder

Seasonal affective disorder (SAD) is a clinical diagnosis accepted in the medical community. Dr. Norman E. Rosenthal, Chief of Environmental Psychiatry Branch of the National Institute of Mental Health, is the researcher credited with discovering SAD.

Onset usually occurs during adulthood (with the average onset occurring at approximately age 23), and is four times more likely to affect women than men. According to the National Mental Health Disorders Association, approximately 10 percent to 20 percent of the population suffers from mild winter SAD, and nearly 5 percent suffer from a more severe form of the disorder.

Two seasonal patterns of symptoms have been identified with SAD: a fall-onset type, also called "winter depression," in which major depressive episodes begin in the late fall to early winter months and remit during the summer months, and a spring-onset type, also called "summer depression," in which the severe depressive episode begins in late spring to early summer.

The following are the most common symptoms of SAD. However, each individual may experience symptoms differently. Symptoms may include: